Tom＿＿＿＿＿＿＿show his exam results to his parents.

A．dare not

B．dared

C．dare to

D．dares not to

平波电抗器铁心柱气隙分散布置，使铁心中的磁通在通过气隙时一部分垂直穿过，一部分由气隙外面环绕，称为环绕磁通。